Combinatorial Capacity

Human language uses a fixed set of meaningful elements (morphemes or words/signs) to produce an open-ended set of meaningful combinations of these elements (words/signs or phrases and sentences). [N.B. this particular definition of “combinatorial capacity” is sometimes referred to as “productivity” (1) or as “recursion” (2), which is defined differently here (cf. “Recursion”).] In primate alarm call systems, the repertoire of elements associated with different predator types is already extremely limited (often to just two or three). (3,4,5) Documented combinations are even more limited and appear to consist of simple juxtaposition of call types. In primate long call systems (and whalesong and birdsong), the combinatorics appear more open-ended by virtue of the duration of the vocalization (as long as 30-40 minutes), but there is as of yet no good evidence for stable associations of any of the individual elements of long call sequences with real-world situations.(6) Despite the apparent success of language-trained apes in acquiring aspects of symbolic and displaced reference, they to date appear incapable of combining the symbols that they may learn in any meaningful way that exhibits stable mappings and internal structure independent of the structure available in trainer input. (7,8) That said, several animal species (bonobos, parrots, border collies, dolphins) have been trained to respond appropriately to commands that incorporate language-like or even linguistic combinatorics. (9)